Wireless communication methods in particular implemented in mobile devices have recently become more popular. Especially when implementing more than one communication method within a single mobile device, such as a mobile phone, and operating the communication methods simultaneously particularly at similar frequencies, then signals related to the communication methods may interfere, compromising the quality of the communication methods. An example of such a scenario is a mobile device, for instance, a mobile phone used for wireless voice over IP via WLAN, while the user of the mobile phone further utilizes a wireless headset based, for instance, on Bluetooth. Then, if the Bluetooth device of the mobile phone transmits a signal, for instance, a burst to the headset, then the WLAN receiver of the mobile phone also picks up the burst. Since Bluetooth and WLAN operate at similar frequency bands, the burst transmitted by the Bluetooth device may corrupt an incoming signal intended for the WLAN receiver of the mobile phone.
V. Aparin discloses in “A Modified LMS Adaptive Filter Architecture with Improved Stability at RF”, Proceedings of ESSCIRC, pp. 235-238, Grenoble, France 2005, and V. Aparin et. al. disclose in “An Integrated LMS Adaptive Filter of TX Leakage for CDMA Receiver Front End”, IEEE Journal of Solid-State Circuits, Vol. 41, No. 5, pp. 1171-1182, May 2006 an LMS adaptive filter to reject leakage of a sending signal into a receiving signal of a Code Division Multiple Access (CDMA) based transmitter. FIG. 1 shows a CDMA transceiver as disclosed by V. Aparin.
The transceiver comprises an antenna 1, a duplexer or diplexer 2, a low noise amplifier 3, an LMS adaptive filter 4, a mixer 5, and a power amplifier 6. The transceiver is configured to operate in full-duplex mode and thus can send signals at the same time while receiving signals.
A sending signal is amplified by the power amplifier 6 and is emitted by the antenna 1. A received signal is captured by the antenna 1 and is amplified by the low noise amplifier 3. The diplexer 2 is used to separate a receive path Rx used for the received signal and a transmit path Tx for the sending signal. A real diplexer 2 does not separate the receive and the transmit paths Rx, Tx ideally, so that a portion of the sending signal leaks into the receive path Rx. Thus, a signal x(t) output by the low noise amplifier 3 comprises, besides the received signal, a signal component related to the sending signal. In other words, the signal x(t) is the received signal corrupted by the sending signal.
The LMS adaptive filter 4 is used to at least approximately generate the uncorrupted received signal from the signal x(t) by filtering out at least approximately the component related to the sending signal from the signal x(t). The output signal of the LMS adaptive filter 4 is denoted as y(t) and is the input signal for the mixer 5.
In order to at least approximately filter out the component related to the sending signal, a reference signal r(t) is coupled out from the transmit path Tx using an appropriate device 7. The reference signal r(t) is related to the sending signal and is input to the LMS adaptive filter 4. The LMS adaptive filter 4 is configured to estimate the component related to the sending signal within the signal x(t) utilizing the reference signal r(t) and then to subtract the estimated component from the signal x(t) in order to generate the signal y(t). The LMS adaptive filter 4 may be trained during an initial calibration procedure based on the least mean square (LMS) method.